Torque transmission device useful as a fixed constant velocity ball joint for drive shafts and method for producing such a joint

ABSTRACT

A torque transmission device such as a fixed constant velocity ball joint constructed as an opposed track joint and a process for producing such a device, in which the curvatures bases of the tracks of the joint deviate in their axial course from the curvatures of the ball contact lines. The process is characterized in that prior to the formation of a longitudinal profile of the joint component, the component is brought to an increased hardness by a hardening process and a diffusion layer is partially or completely removed in the region of the longitudinal profile.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of international patent applicationno. PCT/DE2007/001183, filed Jul. 5, 2007 designating the United Statesof America and published in German on Jan. 10, 2008 as WO 2008/003303,the entire disclosure of which is incorporated herein by reference.Priority is claimed based on Federal Republic of Germany patentapplication nos. DE 10 2006 031 002, filed Jul. 5, 2006; DE 10 2006 037847, filed Aug. 12, 2006 and 10 2007 030 898, filed Jul. 3, 2007.

BACKGROUND OF THE INVENTION

The invention relates to a torque transmission unit having at least onecomponent for transmitting torques via each of two functional areasformed onto the component and causing the torque flow by a formfittingengagement with other elements, at least one of the two functional areasbeing constructed as a profile, such as longitudinal teeth.

Torque transmission units of this type are disclosed, for example, inU.S. Pat. No. 6,872,143 (=DE 102 20 715) in connection with side shaftsand in US 2006/0014587 (=DE 102 37 172) in connection with longitudinalshafts.

In U.S. Pat. No. 6,872,143, two such components are provided for each ofthe fixed, constant velocity ball joints provided on both ends of theside shaft, on each of which different functional areas formed onto theparticular component are provided, which cause the torque flow byformfitting engagement and one of which is constructed as longitudinalteeth.

One component is the joint external part, whose one functional areacausing the torque flow by formfitting engagement is a connection pinhaving formed-on longitudinal teeth, which is provided on the jointexternal part, and whose other functional area transmitting the torqueare the raceways in the joint external part for the balls of the joint.

The second component also having two functional areas for transmittingtorque is the joint internal part having formed-on longitudinal teeth inthe central internal area as one functional area and having formed-onball raceways of the joint internal part as the other functional area.

In the torque transmission unit according to US 2006/0014587, acomponent having two functional areas for transmitting torque is alsoprovided for each of the three joints contained therein, namely a jointinternal part having formed-on longitudinal or spline teeth as onefunctional area and formed-on ball raceways as the other functional areain each case.

In components of this type, i.e., joint parts, for example, the internalteeth are typically broached and the external teeth are typicallyproduced by pounding, milling, or rolling, and the ball raceways areproduced by machining or by a non-chip-forming or chipless technique.

To be able to transmit sufficient torque, at least the ball raceways arehardened. These raceways may be inductively hardened and the remainingarea, i.e., also the longitudinal teeth, may be left at the basichardness. This is advantageous for producing longitudinal teeth, butdoes not permit the high torque values to be transmitted and the desiredservice life to be achieved, which are required in many cases.

The inductively hardened ball raceways, for example, must be machinedhard because of the distortion occurring upon partial hardening afterthe hardening to achieve the acquired precision, i.e., hard milling orgrinding must be performed.

Another known possibility is to first manufacture the teeth in the softstate, to case-harden the entire part, i.e., having formed-onlongitudinal teeth, which results in hardening distortion of both theteeth and also the spline teeth, however, which may only be remedied inthe longitudinal teeth with additional great effort, namely by hardbroaching in the hard layer using corresponding suitable, but costlyspecial machines and tools, for example.

SUMMARY OF THE INVENTION

The present invention was based on the one hand on the object, in torquetransmission devices of the type described above of obtaining highstrengths and thus ensuring the transmission of high torques at highprecisions, i.e., optimum fit and optimum true running, as well asallowing cost-effective and efficient production, and increasing theservice life of assemblies, machines, and devices equipped withcomponents of this type.

Furthermore, the invention relates to torque transmission devices, suchas fixed, constant velocity ball joints as opposed track joints having

a joint external part having external tracks,

a joint internal part having internal tracks,

torque-transmitting balls, which are accommodated in track pairs made ofexternal tracks and internal tracks,

a ball cage having cage windows, in which balls are retained and guidedupon joint deflection,

first external tracks forming first track pairs, in which first ballsare retained, with first internal tracks,

second external tracks forming second track pairs, in which second ballsare retained, with second internal tracks,

the first track pairs and the second track pairs forming ball contactlines having opposing curvatures,

the external tracks and the internal tracks being delimited by externaland internal track bases.

In opposed track joints as are described, for example, in U.S. Pat. No.6,872,143, the ball raceways and/or running channels are produced inpractice by chip removal.

It has already been suggested in U.S. Pat. No. 7,396,284 (=DE 102 09933) that the external tracks or running channels be formed in anon-chip-forming or chipless manner.

The chip-removing production according to U.S. Pat. No. 6,872,143 isprimarily complex, and requires costly machines and long machiningtimes. It also causes significant waste and quality losses in regard tothe strength, because the material flow lines are cut through by themachining in a joint internal or external part produced as a preform byforging.

To produce the ball raceways in joints such as those of U.S. Pat. No.7,396,284 in a chipless or non-chip-forming manner, the prior artdescribes the possibility, for example, of providing hot-cold orwarm-cold processes, a preform being produced within a forgingprocedure, for example, and the required precision being able to beachieved in a cold calibration process.

Because it is an opposed track joint, differing tools each havingopposing ball raceways must already be provided for the production ofthe preform for such a process. The part precision is also limited bythe guiding precision of the machine.

The unavoidable indexing irregularity in the preform also can no longerbe remedied in the following machining steps.

A tool having the same irregularities is also required for thecalibration process for each of the different ball raceways.

The invention is based on the further object of avoiding thesedisadvantages and allowing cost-effective and high-quality production ofinternal and/or external joint parts and thus of fixed, constantvelocity joints, in that investment costs for complex and costlymachines are avoided, tool wear is reduced, and short machining timesare ensured with an optimization of the quality, in particular also inregard to achieving higher torque transmission values. Furthermore, theindexing precision is to be improved and waste-free production, inparticular of the ball raceways, is to be made possible, so thatmachining times, in particular machine run and handling times, arereduced. Moreover, higher carrying capacities are to be achieved andwaste is to be avoided.

A solution according to the invention for the first part of the objectis achieved in that in a torque transmission unit, which has at leastone component having two functional areas for transmitting torque, andone of the functional areas being constructed as a longitudinal profile,in particular as longitudinal teeth, the component as a whole ishardened, but the longitudinal teeth have a lower hardness than theother functional area, but a higher hardness than the base hardness of ajoint external or internal part, i.e., the longitudinal teeth have alower hardness than the ball raceways, but a hardness exceeding the basehardness at least over partial areas of their radial extension.

In particular, hardening with which at least a specific hardening depthresults, i.e., the base hardness of the workpiece is increased at leastapproximately over the height of the teeth, may be advantageous. In anespecially advantageous way, a hardening process connected to adiffusion process, such as cost-effective surface hardening in the formof case hardening with subsequent quenching and annealing, may besuitable, which results in a high boundary hardness and—at least for thecomponents discussed here—a lower hardness, the core hardness, i.e., ahardness exceeding the base hardness, in the areas lying within theareas having boundary hardness. Nitration or boration may also besuitable as the hardening process.

It has been found that after at least approximate removal of the areashaving boundary hardness, e.g., by a lathing process, in the axial areain which the teeth are formed, this may be performed here using themachines and tools under practically identical conditions as themachining of “soft”, unhardened material, i.e., for example, on typicalbroaching-milling-pounding machines or similar machines.

The second functional areas, i.e., the ball raceways here, may be hardmilled and/or ground within the zones of the boundary hardness, as isknown. A very special, separate, and independent aspect according to theinvention, however, is the creation of a component and the provision ofa method for producing such a component, at least one of which isprovided in a torque transmission device, which has two differentfunctional areas for transmitting torque which are formed on thecomponent and cause the torque flow by formfitting engagement, one ofwhich is constructed as longitudinal teeth and the other functional areabeing, for example, the raceways for the balls of a joint, thecomponent, however, in particular one of the functional areas beingproduced chipless and subsequently hardened, in particularsurface-hardened, as described at the beginning, and the componentfurther being distinguished in that the formed-on ball raceways are orwere not subject to machining, the ball raceways are thus in installablestate after the hardening procedure. In particular for such joints,inventive measures according to the claims and/or measures mentioned inthe description may also be applied.

To produce a component of this type, it may be advantageous to subjectthe component as a whole to surface hardening, in particular a casehardening process, with a subsequent quenching and annealing procedure.The hardest area, i.e., the boundary layer and possibly the transitionarea, is partially removed, e.g., by chip removal, thus by lathing, forexample, in the axial area on which the longitudinal teeth are to beapplied, and subsequently the longitudinal teeth are formed in the areabrought to the so-called core hardness by the hardening procedure andthe subsequent annealing.

These longitudinal teeth may, as already noted, be produced inparticular by machining, e.g., by broaching and specifically by “softbroaching”, i.e., using normal tools and machines, because they allowthe broaching in the core hardness in the same way as with parts whichonly have the base hardness.

At relatively low cost and without requiring provision of specialmachines, the invention ensures rapid and efficient production of thelongitudinal teeth with sufficiently high hardness and also acorrespondingly high strength and, by the possibility of using theso-called soft broaching, the production of longitudinal teeth havinghigher precision and service life.

The second part of the statement of the object is achieved according tothe invention by constructing the joint external part and/or the jointinternal part in such a way that the curvatures of the trackbases—viewed in their axial course—at least partially deviate from thecurvatures of the ball contact lines, the term “lines” also comprisingplanar areas or combinations of lines and surfaces in the tracks and/orrunning channels for specific applications. It may be advantageous ifthe track bases—viewed in the axial direction—run partially at leastapproximately axially parallel.

In other words, according to the invention the tracks no longer need tobe completely deformed over the entire axial distance, but rather onlywhere this is necessary to achieve the ball contact lines.

The joint internal part and/or the joint external part are expedientlyproduced chipless as a preform in a forming tool and provided with atleast approximately axially-parallel grooves and projections aspre-formed contours to form the ball contact lines.

The preform may be produced by forging, for example, such as a coldand/or hot forging method or also by other shaping methods, such assintering.

The ball contact lines of the joint internal part and also the jointexternal part may be formed by chipless deformation of the projectionsand/or grooves in a forming tool. This deformation may be performed in acalibration tool, in which the ball raceways and/or contact lines may begeometrically finished-formed, so that they do not need to be machined.

During the production of the ball contact or running lines, along whichthe balls move upon the deflection of the joint, specific axial areas ofthe grooves or groove bases and/or notches formed during the productionof the preform are expediently not deformed by the calibration tool, sothat their structure, which runs at least approximately axially, ispartially maintained over the axial course of the finished externaland/or internal tracks of the joint external part and/or the jointinternal part. This provides the advantage of less deformation work,inter alia.

Furthermore, the invention relates to a method for producing fixed,constant velocity ball joints, which is distinguished in that the tracksof the joint external part and/or joint internal part are produced byreshaping in a preform, i.e., by cold and/or hot reshaping, in thatfirstly at least approximately axially-parallel notches are produced,the ball raceways are subsequently at least approximately finishedgeometrically in opposing directions, preferably also by reshapingtechnology, e.g., in a compression or calibration procedure, withoutmachining being required.

Both the preform and also the opposing course of the ball contact linesmay each be produced in one work step and by cold and/or hot reshaping,it being advantageous if the final work procedure is a calibrationprocedure, so that at least then the ball raceways of the joint part nolonger have to be machined (even after a hardening process, e.g., casehardening).

Due to the production initially of a preform having notches running atleast approximately parallel in the axial direction and subsequentdeformation thereof into ball raceways having the contact and/or runninglines for the balls, first of all waste-free production is ensured andthus cost-effective and efficient production and furthermore highindexing precision is achieved, specifically by the tools themselves.The machine itself does not require precise guiding, because theprojections and/or grooves of the preform, which extend at leastapproximately axially-parallel, have been predefined by a single tooland during the finish forming of the ball run lines, the shaping fingersof the tool practically thread themselves.

Particular advantages result, as already noted, if the preform isproduced in a single tool, because then the indexing precision of thepart itself comes out just as well as the indexing precision of thetool, and this may be very high because the tool is not divided.Furthermore, none of the separate guides for each tool half otherwisenecessary for divided tools are required for such an operation.

Also during the calibration operation, which forms the restriction andthus the ball raceways or running lines from the preform, the guiding ofthe tools relative to one another may be performed by the alreadyexisting, precisely divided preform and therefore a machine havingspecial guiding precision is not necessary. In addition, the preformitself does not have to be inserted in a targeted way into thecalibration tool, because all 8 tracks, for example, are initiallyidentical, and are produced differently from these identical tracks inthe calibration tool.

Furthermore, it may be advantageous to construct and/or produce cagecentering faces in the joint external part according to the presentinvention, as described in U.S. Pat. No. 7,396,284, the entiredisclosure of which is incorporated herein by reference. These cagecentering faces in the external joint may be constructed in such a waythat channels or grooves extending in the axial direction are providedbetween each of the adjacent first and second cage centering faces, thecurvatures of the bases of these channels or grooves at least partiallydeviating in their axial course from the curvatures of the cagecentering faces. These track bases—viewed in the axial direction—mayalso at least partially extend approximately axially-parallel.

Like the grooves and projections for the ball contact lines or raceways,the cage centering faces may also be produced in a preform in a chiplessmanner in a forming tool as adjacent radial projections having a grooveprovided between them which at least runs axially-parallel, the twoprojections each being provided between two adjacent raceways.

This preform may also be produced by forging, for example. The cagecentering faces are advantageously produced in finished form by chiplessdeformation, such as calibration, of the particular projections adjacentto a groove, the cage centering faces adjacent to one another eachrunning originating from one end, e.g., the drive-side end, in thedirection toward the output-side end, approaching the axis of theexternal joint, and the second cage centering faces running originatingfrom the output-side end in the direction toward the drive-side end andapproaching the internal hub axis.

In the same way as described in connection with the raceways, thestructures of the grooves and/or the projections of the preform may alsobe at least partially maintained here.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail hereinafter withreference to illustrative preferred embodiments shown in theaccompanying drawing figures in which:

FIG. 1 shows a torque transmission unit according to a feature of thepresent invention;

FIGS. 1 a and 1 b show a section along line Ia-Ia;

FIG. 2 shows a drive configuration for a motor vehicle having twopartial shafts and an approximately centrally situated cardan joint;

FIG. 3 shows a cross-section through the cardan joint corresponding to asection along line III-III of FIG. 4;

FIG. 4 shows a section along line IV-IV of FIG. 3;

FIG. 5 shows a section along line V-V of FIG. 3;

FIG. 6 shows a section along line VI-VI of FIG. 3;

FIG. 7 shows a section along line VII-VII of FIG. 3;

FIG. 8 shows a view from the direction of the arrow X of FIG. 4;

FIG. 9 shows a view from the direction of the arrow Y of FIG. 4;

FIGS. 10-13 show a joint internal part as unfinished and finished parts;

FIGS. 14-18 show a joint external part as unfinished and finished parts.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The fixed constant velocity joint 101 according to FIG. 1 comprises ajoint internal part 102 having ball raceways 103, as well as a jointexternal part 104 having ball raceways 105 formed thereon in a knownway. Balls 106, which transmit the torque between internal and externalparts, are provided between the ball raceways 103 and 105 of jointinternal and external parts 102 and 104. A cage 107 is used for guidingthe balls.

The joint internal part thus has functional areas for torquetransmission in the form of the longitudinal teeth 108 on the one handand in the form of the ball raceways 103 on the other hand.

The joint internal part may advantageously be a forged part having acentral recess 108 a provided for the formation of the teeth. The ballraceways 103 may be produced, for example, by machining or chiplessly.

The joint internal part is initially subjected as a whole to a surfacehardening, in particular a case-hardening process having quenching andsubsequent annealing, for example. Before the formation of the teeth108, the area of greatest hardness of the recess 108 a is removed, forexample, by machining, such as by lathing.

The internal teeth 108 may then also be produced by machining, forexample, by broaching in a very simple and cost-effective work stepwhich ensures high precision. The ball raceways 103 may be ground—beforeor after the production of the teeth.

In the construction of the teeth 108 according to FIG. 1 or teeth on apin on the internal joint—or, if the external joint part 16 has teeth,i.e., for example, if external teeth are provided on a pin or internalteeth are provided on a sleeve-shaped attachment—it may be advantageous,as already noted, if the part is case-hardened as a whole before theformation of these teeth. One possibility for the construction of oneembodiment of such a joint according to the invention is shown in FIGS.1 a and 1 b, which depict an enlarged detail view corresponding toarrows Ia-Ia of FIG. 1.

FIG. 1 a shows the detail in a state after the hardening having theboundary layers 111 and 112 and the transition areas 113 and 114. Thearea of the core hardness is shown by 115. According to FIG. 1 b, atleast the area of the highest hardness 112 is removed, e.g., by lathing,and the transition area 114 may be at least partially removed, however,as shown in FIG. 1 b, it is entirely removed, so that the teeth 116 liecompletely in the area of the core hardness 115.

It is advantageous if the surface hardness of the boundary layers 111and 112 is between 55 and 64 HRC, preferably in the range from 60±3 HRC.The case hardening depth is expediently between 0.3 and 2 mm (forboundary hardness 550 HV, corresponding to 52.3 HRC), but preferably inthe range around 1 mm, here for a diameter of the balls 106, whichtransmit the torque in the magnitude of approximately 13 mm. The corehardness is expediently in the range from 20 to 50 HRC, preferably from30 to 40 HRC. The hardness of the teeth—at 350 HV here—is significantlyhigher than the original base hardness of the starting material, in thiscase less than 200 HV.

In the same way, joint external parts having external teeth provided ona pin may also be produced according to the invention, the externalteeth also being able to be produced in a cost-effective way whichensures high strength and high torque transmission values by machiningor reshaping processing, e.g., by pounding, milling, rolling, or thelike in an area which was previously hardened and in which the hardestareas were removed before the formation of the teeth. In a jointinternal part, a pin may also have external teeth or a joint externalpart may have internal teeth.

The described features according to the invention are not restricted tothe torque transmission devices, which were described in detail above,but rather also extend to other torque transmission devices in which acomponent has two functional areas for transmitting torques byformfitting engagement with other elements.

The driveshaft 1 shown in FIG. 2 is constructed here as a longitudinaldriveshaft of a motor vehicle and comprises two partial shafts 2 and 3,which carry connection parts 4, 5 on their free ends. These connectionparts are constructed as flexible rubber couplings, although cardanjoints may also be fastened to the cited partial shafts 2 and 3 in theirplace, as described in US 2006/014587 or U.S. Pat. No. 6,893,352 (=DE100 32 853).

The two partial shafts 2 and 3 are connected to one another via a cardanjoint 8, which is shown in various sectional illustrations in FIGS. 3through 9, approximately in the middle of the drive configuration 1. Inaddition, FIG. 2 shows that the left partial shaft 2 is fastenable tothe underbody of a motor vehicle via an intermediate bearing 6 and aretainer 7 situated thereon.

As can be seen in particular from the sections according to FIGS. 3through 7 and FIG. 10, which show the cardan joint 8 not connected tothe partial shafts 2 and 3, the cardan joint primarily comprises anessentially hollow-cylindrical external hub 16, in which an internal hub10 is situated coaxially. While the first partial shaft 2 may have itsexternal spline teeth inserted into internal spline teeth 11 of theinternal hub 10, the connection of the external hub to the secondpartial shaft 3 is performed in the present exemplary embodiment by awelded bond, for which a welding flange 12 is constructed on a driverhousing 9. The external hub 16 is accommodated in the driver housing,and is enclosed in a formfitting way in a receptacle area 17.

First external ball running channels 19 for a first array of balls 14and further external ball running channels 19 a for a second array ofballs 14 a are provided on the interior side of the external hub 16.Webs 20 are located between them in each case.

First internal ball running channels 18 for the first array of balls 14and further internal ball running channels 18 a for the second array ofballs 14 a are provided on the exterior side of the internal hub 10.Webs 28 are located between these ball raceways in each case.

The track base of the ball grooves is identified in each case by 18′,19′ and 18 a′ and 19 a′.

The internal hub 10 has an internal hub axis I and an external face 24.As can be seen from FIGS. 4, 8, 9 in particular, the first internalrunning channels 18 and the second internal running channels 18 a aresituated distributed alternately around the internal axis I, the firstinternal running channels 18 running here originating from thedrive-side end 2 a in the direction toward the output-side end 3 a, andthe internal running channels and their track base 18′ moving away fromthe internal hub axis I; as can be seen from FIGS. 5 and 8, 9 inparticular, the second internal running channels 18 a run here from theoutput-side end 3 a in the direction toward the drive-side end 2 a,these second internal running channels and their track base 18 a′ movingaway from the internal hub axis I here. The first and second internalrunning channels having their opposing first and second external runningchannels may also be situated in a sequence other than alternately withone another and may have other courses than described and shown here,e.g., a course first moving away from the corresponding axes andsubsequently approaching them again.

The external hub 16 has an external hub axis II and an internal contour,in which first ball running channels or raceways 19 for the first arrayof balls 14 and second ball running channels or raceways 19 a for thesecond array of balls 14 a are situated distributed alternately aroundthe external hub axis II and in each case the first internal runningchannels 18 are opposite to the first external running channels 19 andthe second internal running channels 18 a are opposite to the secondexternal running channels 19 a and form a pair with them in each case,the first external running channels 19 running originating from thedrive-side end 2 a in the direction toward the output-side end 3 a, andthe external running channels 19 and their track base 19′ approachingthe external hub axis II, and, furthermore, the second external runningchannels 19 a run originating from the output-side end 3 a in thedirection toward the drive-side end 2 a, and the second external runningchannels 19 a having their track base 19 a′ approach the external hubaxis II (FIGS. 4 and 5).

In an annular cage 15 having an at least sectionally spherical externalface 26 (see FIGS. 3, 6, and 7 in particular), which is situated betweenthe internal hub 10 and the external hub 16, radial windows 27, in whichthe balls 14, 14 a are guided (see also FIGS. 4, 5) are provided inaccordance with the number of the balls 14, 14 a and/or running channelpairs 18, 18 a, 19, 19 a. The cage 15 is centered in the external hub 16via its external face 26, more precisely via the two centering areas 26a.

Webs 20 are provided between the balls in the internal face of theexternal hub 16, as already noted. As may be seen in particular inconnection with FIGS. 4, 6, 8, and 9, viewed from the drive-side end 2 aand around the circumference, these webs have insertion contours 16 aprimarily provided on both sides of the ball grooves 19 for the balls 14for the axial insertion of the cage 15 into the external hub 16. Theinsertion contours 16 a originate on the driver side 2 a from a diameterwhich at least approximately corresponds to the external diameter of thecage 15.

Viewed in the axial direction, starting from the drive-side end 2 a ofthe joint, these insertion contours merge after at least approximatelyhalf of the axial length into the cage centering faces 16 b on the jointexternal part for the cage and are inclined in the direction toward thecage centering axis III (see FIGS. 4, 6, 8, and 9). The cage centeringfaces 16 b are correspondingly adapted as crowned to the sphericallyconstructed contact faces of the ball cage.

Viewed in the axial direction, originating from the output-side end 3 aof the joint, these insertion contours 16 c merge after at leastapproximately half of the axial length of the cage into the second cagecentering faces 16 b on the external hub for the cage. From there, theyrun inclined in the direction toward the cage centering axis III. Thesecond cage centering faces 16 b are correspondingly adapted as crownedto the spherically constructed contact faces 26 b of the ball cage, likethe first faces.

As already noted, FIGS. 10-13 show a joint internal part as theunfinished part and finished part R10 and F10 and FIGS. 14-18 show thejoint external part as the unfinished part and finished part R16 andF16.

The preform R10 according to FIG. 10 is a forged part having four pairsof projections or webs R20, R20 a, which are distributed uniformlyaround the circumference and are constructed at least approximatelyuniformly, between which grooves or notches R18, R18 a having groovebases R18′ and R18 a′, which run at least approximately axiallyparallel, are provided.

The preform R10 may also be produced, as already noted, using a hot-coldor warm-cold process, for example, or also as a sintered part.

The running channels F18, F18 a apparent from FIGS. 11, 12, and 13 aredeformed from the projections or webs R20, 20 a by calibration in a toolwhich consists of two tool halves having plungers running in oppositedirections to form the opposing running channels F18, F18 a, using acold deformation method, in particular by calibration.

The groove bases R18′ and R18 a′ according to FIG. 10 remain at leastpartially maintained even after the calibration, as do partial areasF18″, F18 a″ according to FIGS. 11-13 from the lateral flanks R18″ andR18 a″ previously contained in the preform R10. Only the crosshatchedsections F18′″ and F18 a′″ were deformed, as can be seen in particularfrom FIG. 11. The faces F18′″ and F18 a′″ are deformed in such a waythat ball running lines or ball contact lines F18 b and F18 b′ arise,along which the balls move upon the deflection of the joint.

Furthermore, it can be seen in particular in connection with FIG. 13that the ball raceways F18 b and F18 b′ and the remaining areas of thegroove bases F18′ and F18 a′ have different curvatures.

FIGS. 14-18 show unfinished and finished parts of the external joint R19and F19, FIGS. 17 and 18 showing FIG. 16 along lines A-A and B-B.

The preform R16 according to FIG. 14 is produced here as a forged parthaving first and second projections or webs R28, R28 a and R28′, R28 a′,which extend radially inward. The projections R28 and R28 a, which runat least approximately axially-parallel, are designed as at leastapproximately mirror-image, like the projections 28′ and 28 a′.

The projections R28 and R28 a each enclose a first groove or notch R19between them, which runs at least approximately axially-parallel, as theprojections R28′ and R28 a′ enclose a second groove or notch R19 abetween them. The projections R28 a and R28′ as well as R28 a′ and R28each enclose a third groove R31 between them.

The grooves R19 and R19 a each have groove bases R19′ and R19 a′ and thegrooves R31 each have groove bases R31′. The grooves R19 and R19 a alsohave side flanks R19″ and R19 a″.

The joint external part is produced as a finished part F16 by acalibration procedure. The first and second ball running channels F19and F19 a of FIGS. 15-18 are deformed from the side flanks R19″ and R19a″ of FIG. 14.

The groove bases R19′, R19 a′ of FIG. 14 are maintained at leastapproximately over the axial extension thereof as the track bases F19′.Only the crosshatched sections F19″ and F19 a″ in FIGS. 17 and 18 aredeformed of the side flanks R19″ and R19 a″ and the ball contact linesor ball running areas F19 b and F19 b′ are thus formed.

It is also apparent here that the curvature of the groove bases F19′differs from that of the contact lines F19 b and F19 b′.

The second channels F19 a are produced in the same way as the firstrunning channels F19, but in the opposite direction, i.e., restricted tothe channels F19.

On both sides of the groove F19, insertion contours F16 a running atleast approximately in the axial direction are produced from the firstprojections R28 and R28 a, advantageously by the same calibrationprocedure in which the contours F19, F19 a, F19′″, F19 a′″, F16 b, F16b′ are generated.

In the further axial course of the insertion contours F16 b, the cagecentering areas F16 b are provided on both sides of each channel F19, astepped projection or transition area being provided between thecontours F16 b and F16 a.

The cage centering areas F16 b and F16 d are adapted to the sphericalcontact faces 26 b of the ball cage 15.

In the same way, but with opposing restriction, the cage centering facesF16 d and the insertion faces F16 c are produced and/or constructed onboth sides of the channels F19 a.

The foregoing description and examples have been set forth merely toillustrate the invention and are not intended to be limiting. Sincemodifications of the described embodiments incorporating the spirit andsubstance of the invention may occur to persons skilled in the art, theinvention should be construed broadly to include all variations withinthe scope of the appended claims and equivalents thereof.

1. A torque transmission device comprising at least one component havingtwo functional areas for transmitting torque via respective differentfunctional areas which are formed on the component and which achievetorque transmission by formfitting interengagement, wherein: one of saidfunctional areas is a longitudinal profile; prior to formation of thelongitudinal profile, the component as a whole is brought to a hardnesswhich is higher than a base hardness of said component by a hardeningprocess which produces at least one boundary layer having a depth withhighest hardness and below said boundary layer a layer with corehardness, said core hardness being higher than said base hardness andlower than said highest hardness, and during subsequent formation of thelongitudinal profile, the entire depth of the at least one boundarylayer is removed in the area of the longitudinal profile down to saidlayer with core hardness.
 2. A device as claimed in claim 1, whereinsaid longitudinal profile comprises longitudinal teeth.
 3. A device asclaimed in claim 1, wherein the hardening process is case hardening. 4.A device as claimed in claim 1, wherein the hardening process isquenching and annealing.
 5. A device as claimed in claim 1, wherein saidhardening process produces said at least one boundary layer and at leastone transition area.
 6. A device as claimed in claim 5, wherein said atleast one boundary layer and said transition layer are at leastpartially removed.
 7. A device as claimed in claim 1, wherein said atleast one boundary layer is at least partially removed by lathing.
 8. Adevice as claimed in claim 1, wherein said longitudinal profile isformed by broaching.
 9. A device as claimed in claim 8, wherein saidlongitudinal profile is formed by soft broaching.